Build instructions don't work out of the box for Mac OS X

Nobody has claimed this yet.

I tried to follow the build instructions to install CIRCT in my Mac (OS X Sequoia 15.6.1) but they don't quite work out of the box.

One issue is the linker, I add to specify `-DLLVM_ENABLE_LLD=OFF`.

Another issue seems to be confusion about `llvm::Type` vs. `mlir::Type` e.g. in `PruneZeroValuedLogic.cpp`
Perhaps in such files one should write:

```cpp
types, [](mlir::Type type) { return ExportVerilog::isZeroBitType(type); });
```

instead of:

```cpp
types, [](Type type) { return ExportVerilog::isZeroBitType(type); });
```

to qualify the `Type`?

Or do something like this:

```cpp
using mlir::Type;
using mlir::Value;
```

I got around this problem by first building LLVM that comes in the submodule.
Then I built with:

```
cmake -G Ninja . -B build \
-DCMAKE_BUILD_TYPE=RelWithDebInfo \
-DLLVM_ENABLE_ASSERTIONS=ON \
-DMLIR_DIR=$PWD/llvm/build/lib/cmake/mlir \
-DLLVM_DIR=$PWD/llvm/build/lib/cmake/llvm \
-DLLVM_TARGETS_TO_BUILD=host \
-DLLVM_ENABLE_PROJECTS=mlir \
-DLLVM_EXTERNAL_PROJECTS=circt \
-DLLVM_EXTERNAL_CIRCT_SOURCE_DIR=$PWD \
-DLLVM_ENABLE_LLD=OFF \
-DCIRCT_SLANG_FRONTEND_ENABLED=ON
```

I had to specify ` -DLLVM_ENABLE_LLD=OFF`.

Perhaps worth updating the documentation, or build, to give a smoother install experience for Mac OS X?

Reproduce the Mac OS X Sequoia 15.6.1 build using the documented CMake/Ninja command, including the reported LLVM_ENABLE_LLD setting and the Type qualification issue in PruneZeroValuedLogic.cpp. Compare the documented steps with the working command in the issue; done means the build works out of the box or the instructions clearly document the required changes.

Written by the indexing model from the issue text.